A spin or staple-fiber band is basically a thick yarn made of a multiplicity of long staples. When made from polyester the staple must be textured so that the normally smooth and straight monofilaments hold together, giving the staple-fiber band an excellent band.
Such a band is made by first pulling synthetic-resin filaments, typically of polyester, from their spinnerets and cooling them to form filament bundles, hereinafter referred to as rovings, which are set aside or stored. The rovings, are wound up with limited stretching or preorienting because winding-type takeups can typically only operate as a peripheral or filament-feed speed of at most 2000 m/min (about 75 miles/hour), which speed generally corresponds to the speed at which the filaments exit from the orifices of the spinneret. As is known the stretching and the resultant preorienting of the individual filaments depends from the double breaking which in turn is a function of the overfeed or difference between the spinning speed and the takeup speed. Double breaking is the difference of the breaking index in the longitudinal and transverse directions of the filaments.
As a rule the stored rovings are plied to so-called spin cables and are subsequently fully oriented, that is they are stretched to have a residual stretch of between 18% and 30% so they can only be stretched to this extent before the filaments will break. This necessitates an intermediate treatment of the spin cable in a stretching and texturing machine. During such intermediate treatment the spin cable traverses several stretchers with intermediate heaters, then a washing and drying stage, and finally passes through a texturing device followed by a thermofixing unit. The thus fully oriented and almost stretched-out spin cable is then set aside in boxes.
Subsequently the cables are delivered to a tear converter which longitudinally stretch-tears and then textures the spin cable to so-called spinning bands or staple-fiber bands. The stretch and crimping stages preceding the tear converter serve mainly to prevent the filaments from tangling during layup or storage. If the filaments do not remain perfectly parallel in the spin cable it becomes impossible to tear them into perfect spin bands or staple-fiber bands.
Obviously this production technique is fairly complex and quite expensive. Hence it is known to make textured polyester yarn by the set-texturing method with false twist. In this arrangement a roving of filaments of low crystalinity is made by pulling the polyester filaments from the spinnerets with a takeup speed of at least 2750 m/min and is thereafter set-textured to an extent between 1:1.3 and 1:2. The filaments are then thermofixed at above 200.degree. C. so that filament breakage is largely avoided. This procedure does not appreciably affect the production of spinning bands from polyester filaments.